In the field of optics, light may be manipulated to change the end effect seen through a lens. For example, in cameras, filters are commonly used to modify the image recorded. Conventional lens filters are planar (flat) and are generally either screw-on or holder type (slot drop-in, square, or rectangular types). Drop-in type filters are typically positioned behind the lens, so the filter would rest between the lens and the body of the camera. Sometimes, since a flat filter is mounted in front of the lens with rings, the mount is in the optical path way and vignetting occurs.
These kinds of problems can be magnified when working with a fisheye lens. For example, conventional lens filters may be very wide and cumbersome resulting in being caught in the extremely wide field of view of a fisheye lens, thus interfering with the image.
As can be seen, there is a need for a lens filter that can be used with a fisheye lens without interfering with the field of view.